A modal verb or auxiliary verb is a verb, which modifies another verb, so that the modified verb has more intention in its expression. In essence the modal verb expresses modality, the way in which something is being said. Modal verbs are common in most languages of Germanic origin, including English.
Typical modal verbs in English express possibility or necessity. Verbs like may or might are used to suggest that you are possibly going to do something but haven’t quite committed to the action yet. The statement, I might go to the movies is different than the statement I am going to the movies. In the former statement you are expressing the possibility of going to see a movie, and in the latter you express the decided intent of your action to see a movie. The modal verb might or in variant form may helps qualify and modify the verb go.
Other examples of the modal verb in English include can, shall, will, must, and dare. You could state I’m going to work, with no modification, or use modality if you were indecisive, I should go to work or needed to express the importance of working I must go to work. Each use of a modal verb changes the meaning of the sentence. If you should do something, you’re expressing its importance, but perhaps a bit of reluctance. If you must do something, you’re expressing that it’s very important. While all these sentences seem similar, modality affects and creates shades of meaning.
Sometimes a modal verb is used on its own, and the modified verb is implied rather than stated. Consider the following example:
Would you like to share my candy bar?
I shouldn’t.
Obviously, the second speaker in replying means he or she shouldn’t share the candy bar. Perhaps he is on a strict diet. The verb should, expressed in the negative as should not modifies the verb share even though this is not explicitly stated. Similarly statements like I would, I could, I must, I shall, may be used without an additional verb, though that additional verb or action is implied.
Modal verbs lend texture and meaning to language. They can qualify statements, express intent, express need, or suggest possible actions. As a part of the English language, and Dutch and German, they’re valuable to understand since they add color and interest to statements that might otherwise seem bland or unclear.